As we build up light rays, the shape of the envelope begins to emerge. The only difference between this diagram and the physical system is that here, the overlap makes a dark envelope, whereas in the cup the overlap makes a bright envelope

Antigoni is a PhD student at UCL working on Boundary Element Methods for electromagnetic scattering.
More from Chalkdust
(Not) squaring the circle
Sam Hartburn attempts the impossibleCan computers prove theorems?
And will we soon all be out of a job? Kevin Buzzard worries us all.Page 3 model: Crowd control
Modelling a Saturday afternoon on Oxford StreetCreating hot ice
We created hot ice from scratch, a solution that remains liquid even below its freezing point!Curiouser and curiouser!
Some surprising mathematical factsFind your perfect partner
Find your perfect partner with this wonderful tree diagram!